Several measuring instruments are known in the art which are commonly used to measure or monitor an electronic signal or waveform. The electronic signal or waveform may be present, for example, on any one of the pins of an integrated circuit (IC) package, or on leads or terminations of various other circuit components.
Some measuring instruments, such as digital multimeters, measure a single signal or electronic component value at a particular instant of time during a typical measurement operation. In contrast, other measuring instruments, for example an oscilloscope or a spectrum analyzer, measure a set of signal values over a period of time during a measurement operation, wherein the set of values constitutes a waveform. Hence, for purposes of the present invention, "signals" are differentiated from "waveforms" in that the former is represented as a single value, whereas the latter includes a set of individual signal values at different instances of time. The present invention is directed particularly to measuring instruments which have the capability to automatically acquire and store measurements of waveforms.
Waveform measuring instruments typically include a video display for illustrating a two-dimensional temporal or spectral representation of the measured waveform. For example, an oscilloscope typically measures and displays the amplitude of a waveform with respect to time, while a spectrum or network analyzer processes the amplitude-versus-time information of a waveform to display the frequency components of the waveform. Some oscilloscopes may also have the capability to display the amplitude information of a first waveform on a first axis versus the amplitude information of a second waveform on a second axis. Hence, for purposes of the present invention, "video display" refers to a visual display of a waveform measuring instrument on which at least one two-dimensional representation of one or more waveforms may be illustrated. Specifically, each representation displayed by the video display has at least two axes or "dimensions," for example, a vertical axis and a horizontal axis.
Waveform measuring instruments are known which have the capability to store in memory one or more two-dimensional representations of probed waveforms for displaying the representations at some later time. As discussed above, such waveform measuring instruments must measure and store a set of signal values to represent a waveform, as opposed to merely measuring a single value. The process of acquiring and storing a waveform measurement using such instruments typically requires an operator to apply, and in some cases hold, a measurement probe to a waveform source, to watch the graphic display of the measuring instrument to view the probed waveform, and to wait until the display indicates that the probed waveform has stabilized. Once the waveform has stabilized, the operator must often specifically instruct the measuring instrument to acquire a measurement of the probed waveform.
Typically, waveform acquisition is accomplished by "sampling" the waveform for some period of time, or "waveform acquisition period." During a waveform acquisition period, the measuring instrument may collect several "sample sets" of values, each sample set including a number of individual signal values necessary to represent the waveform on the video display. For example, a particular video display may be designed to have a horizontal resolution of 500 points in a given time frame to represent a waveform. In this case, each sample set would include 500 individual signal values dispersed in time throughout the time frame represented on the video display. The waveform acquisition period is often determined arbitrarily by the operator manually stopping or "freezing" the acquisitions, perhaps after some desired number of sample sets have been acquired.
After the operator instructs the instrument to stop acquisitions, the operator may in some cases further instruct the measuring instrument to store one particular or "selected" sample set representing the probed waveform, based on the acquired sample sets. This "acquire and store" instruction process is often accomplished by the operator pressing one or more buttons on an operator interface panel of the measuring instrument. Generally, both software routines executed by a processor in the measuring instrument, as well as hardware circuitry, initiate the acquire and store processes by interpreting the selections made by the operator via the buttons of the operator interface panel.
In contrast to conventional acquisition and storage of a waveform measurement as outlined above, a measuring instrument such as a digital multimeter typically measures and displays, in alpha-numeric form, only a single value associated with a signal or circuit component at a particular instant of time, as opposed to a set of values. Some digital multimeters may additionally have a limited ability to store a single signal measurement to be recalled and displayed numerically at a later time, or may sound a "beep" to indicate that a particular measurement is ready for observation on the alpha-numeric display. Digital multimeters, however, do not acquire and store sets of values corresponding to two-dimensional representations of waveforms, and do not display stored waveform representations on a video display, as do measuring instruments such as oscilloscopes and spectrum analyzers.
With respect to the electrical connection of a waveform measuring instrument to a waveform source, various terminations or measurement probes are known for placing a wire or cable attached to a measuring instrument in contact with a waveform source. Some terminations, for example, a probe with a fine "tip," require an operator to hold the termination to the waveform source during a measurement. This requirement may pose particular challenges to the operator during conventional manual waveform measurement acquisition and storage operations, as discussed further below.
One problem encountered during manual waveform measurement operations relates to measurement probe "slippage." This problem may be particularly exacerbated by ongoing improvements in semiconductor and printed circuit board technology. For example, with continued advances in semiconductor fabrication technology, the size of integrated circuits (ICs) becomes progressively smaller. One consequence of reduced IC package size is that the connection terminals or "pins" of the IC are smaller and are closer together, or more densely packed. The packing density and size of IC pins is referred to as "lead pitch." Reduced IC package size also results in printed circuit boards that are more densely occupied by IC chips and other circuit components.
In view of the foregoing, it is to be appreciated that in many instances, acquisition and storage of waveform measurements requires careful application of a measurement probe to a waveform source in order to avoid probe slippage. In such cases, the operator may choose to summon an assistant to perform the manual "stop acquisition and store" functions so that the operator's attention is not diverted from the probe in contact with the waveform source. Examples of potentially challenging waveform measurements include using a fine tip probe on densely packed printed circuit boards having ICs with a small lead pitch, as discussed above, or applying a measurement probe to an IC or a component in a difficult to reach position.
Alternatively, to facilitate the stop acquisition and storage functions and alleviate the need for an assistant, some known measurement probes are equipped with a button to allow the operator to "remotely" perform these functions, in lieu of a button on an operator interface panel of the measuring instrument. Other more elaborate schemes are known for facilitating remote operator instruction of a measuring instrument, some of which employ, for example, a foot pedal or a sound sensitive trigger, such as a voice recognition device, so that the operator may indicate to the measuring instrument to stop acquisitions and/or store an acquired waveform measurement without having to touch the measuring instrument itself.
The above alternative solutions for remotely acquiring and storing a waveform measurement often suffer several disadvantages, however, in that 1) they nonetheless require the operator to look at the video display of the measuring instrument to determine if a probed waveform has stabilized, and 2) the acquisition and storage operations are still performed manually, thereby requiring manual action by the operator or an assistant. This need for the operator to monitor the display and to perform manual operations, either remotely or proximately with the measuring instrument, limits the operator's ability to concentrate on the measurement probe, or to perform some other task during a measurement. In particular, while the operator's attention is diverted from the measurement probe to the video display or the manual operation, especially in the case of a fine tip probe, the probe may slip off of the pin, lead, or termination carrying the waveform of interest.
The risk of accidental probe movement may be especially aggravated in the case of an operator pushing a stop acquisition and/or storage button on a probe equipped with such a button. As discussed above, as the lead pitch on integrated circuits becomes smaller and the component density of printed circuit boards increases, any disturbance of measurement probe placement poses a greater risk of causing damage to a circuit, by contacting or "shorting" multiple pins or component leads with the probe while the operator looks away from the probe to observe a visual display, or pushes a button to stop sample acquisition and store a waveform measurement.